A conventional endless rectilinear motion rolling guide unit has a structure as shown in, e.g., Japanese patent application No. 59-254067 (Japanese patent application disclosure No. 61-136018) which has been proposed by the same applicant as this invention. In a track member having a U-shaped cross section, a table is located inside of a bed and an endless circulating passage for balls is formed around the wall surface of the table.
According to this structure, in the case of reducing a width of bed to miniaturize the linear motion rolling guide unit (for example, a width of linear motion rolling guide unit is set to about 10 mm), it is physically impossible to keep a space enough to form a pair of endless circulating passages in the table. Or, in order to assure the space of the endless circulating passages, a thickness of table in the track groove portion must be thinned. Thus, there is a drawback such that the rigidity of linear motion rolling guide unit deteriorates.
On the other hand, since the balls locating in the track groove are exposed from the upper portion, foreign matters easily enter the track groove portion, causing the linear motion rolling guide unit to be damaged early.
As mentioned above, the conventional sheet-metal type endless rectilinear motion rolling guide unit has a light weight and a high accurate moving performance but, contrarily, has drawbacks such that the width of whole linear motion rolling guide unit cannot be narrowed and the portions which are difficult to be handled still exist.